Oscillators and demodulators provided to radar apparatuses may deteriorate as being used, and be damaged due to intense signals from outside. Therefore, there have been cases where a radar performance monitor is provided to such a radar apparatus so as to check whether a transmission power and a reception sensitivity of the radar apparatus are sufficient.
A radar performance monitor receives a transmission signal transmitted by the radar unit of the radar apparatus, and transmits a response signal to the radar unit. The response signal is analyzed and the result thereof is used for, for example, confirming the performance of the radar apparatus. JP2011-043351A discloses such kind of radar performance monitor.
The radar performance monitor disclosed in JP2011-043351A transmits, as a response signal, a signal of which a frequency continuously changes within a predetermined frequency range including a reception band of the radar unit (so-called chirp signal). With this configuration, a transmission band of the response signal is prevented from being out of the reception band of the radar unit even when the frequency of the response signal is changed, for example.
Meanwhile, in recent years, pulse-compression radar apparatuses have been known, which have configurations of transmitting, as a transmission signal, a signal of which a pulse length is comparatively long and a frequency continuously changes, and performing a pulse compression when the signal is received. As the transmission signal of the pulse-compression radar apparatus, not only a signal of which a frequency changes linearly (linear signal), but also a signal of which a frequency changes non-linearly (non-linear signal) may be used.
Here, with the conventional radar performance monitors provided to pulse-compression radar apparatuses where a non-linear signal is transmitted therefrom, it has been thought that a response signal similar to a transmission signal needs to be transmitted because in a case where a non-linear transmission signal is transmitted, if a frequency of the transmission signal varies from that of the response signal, a signal of which a peak is dropped (or with no peak) will be detected even if the radar unit performs a pulse compression.
Therefore, the radar performance monitors have been required to include a configuration for generating the non-linear transmission signal (e.g., a D/A converter or a mixer). Moreover, the radar performance monitors have been required to receive a reference signal from the radar unit to match the frequency of the transmission signal with that of the response signal. As described above, the radar performance monitors provided to the pulse-compression radar apparatuses where the non-linear signal is transmitted therefrom have the extremely complicated configurations.